Q&A - PSLE Math

[jojoberry]

u are posting in the wrong thread - there's a thread Q&A for Px Maths for each level...

[edlynnalexander]

Pls help! Thank-you!

[ozora]

need some help in this question.
there were 640 stamps in 2 boxes altogether.
1/3 of the stamps are transferred from box A to box B.
Then 1/3 of the stamps in box B are transferred to box A.
As a result, the number of stamps in box B is 1/3 of the number of the stamps in box A.
Find the number of stamps in box A at first

[ozora]

Pls help! Thank-you!

May I know how do u assume the 5/5 units?

[alfretztay]

Pls help! Thank-you!

May I know how do u assume the 5/5 units?

I would solve the above problem as follows :

At first :
A -> 10u + 200
J -> 10u

After A gives 60% to J :
A -> 4u + 80
J -> 10u + 6u + 120 = 16u + 120

After J gives 25% to A :
A -> 4u + 80 + 4u + 30 = 8u + 110
J -> 12u + 90

12u + 90 – (8u + 110) = 200
4u -> 220
1u -> 55
55 x 10 + 200 = 750

Ans : 750 books.

[alfretztay]

need some help in this question.
there were 640 stamps in 2 boxes altogether.
1/3 of the stamps are transferred from box A to box B.
Then 1/3 of the stamps in box B are transferred to box A.
As a result, the number of stamps in box B is 1/3 of the number of the stamps in box A.
Find the number of stamps in box A at first

I would solve the above problem as follows :

640/4 = 160
Working backwards,

A : B
480 : 160
-80 … +80
—– … —–
400 … 240
+200 … -200
—– … ——
600 … 40
…
Ans : 600 stamps.

[alfretztay]

Pls help!

I would solve the above question as follows :

5(B + C) = 4A
4A = 5B + 5C
8A = 10B + 10C
20A = 25B + 25C
A/6 = B/5 + C/3
5A = 6B + 10C
20A = 24B + 40C
3A = 4B = 60C
1A -> 20C
1B -> 15C
area of A : B : C -> 20 : 15 : 1

Ans : 20 : 15 : 1

[ozora]

need some help in this question.
there were 640 stamps in 2 boxes altogether.
1/3 of the stamps are transferred from box A to box B.
Then 1/3 of the stamps in box B are transferred to box A.
As a result, the number of stamps in box B is 1/3 of the number of the stamps in box A.
Find the number of stamps in box A at first

I would solve the above problem as follows :

640/4 = 160
Working backwards,

A : B
480 : 160
-80 … +80
—– … —–
400 … 240
+200 … -200
—– … ——
600 … 40
…
Ans : 600 stamps.

thanks. and thanks for the previous question as well

[ttlkbs]

Pls help!

I would solve the above question as follows :

5(B + C) = 4A
4A = 5B + 5C
8A = 10B + 10C
20A = 25B + 25C
A/6 = B/5 + C/3
5A = 6B + 10C
20A = 24B + 40C
3A = 4B = 60C
1A -> 20C
1B -> 15C
area of A : B : C -> 20 : 15 : 1

Ans : 20 : 15 : 1

[ttlkbs]

Pls help! Thank-you!

May I know how do u assume the 5/5 units?

I would solve the above problem as follows :

At first :
A -> 10u + 200
J -> 10u

After A gives 60% to J :
A -> 4u + 80
J -> 10u + 6u + 120 = 16u + 120

After J gives 25% to A :
A -> 4u + 80 + 4u + 30 = 8u + 110
J -> 12u + 90

12u + 90 – (8u + 110) = 200
4u -> 220
1u -> 55
55 x 10 + 200 = 750

Ans : 750 books.[/quote]

Thank-you to both Edlynnalexander and Alfretztay.
The correct answer is 750.